1. Field of the Invention
This invention relates to a drying control device for printed paper drying apparatus which evaporates the solvent in ink by blowing hot air onto the printed paper. More particularly it relates to a hot air heating type drying apparatus for a rotary printing press which evaporates the solvent in ink by feeding printed paper into a drying apparatus body having a negative pressure and by blowing hot air onto the paper. The apparatus according to this invention can be applied to exhaust gas disposal apparatus for solvent-containing substances in the production process of plastic film and the like. Still more particularly, this invention relates to a paper temperature control device of drying apparatus for a rotary printing press.
2. Description of the Related Art
A conventional drying apparatus for a printing press will be described with reference to FIG. 13. Reference numeral 1 denotes a drying apparatus body, 2 denotes printed paper, 3 denotes a hot air blowing nozzle provided in the drying apparatus 1, 4 denotes a burner for heating the hot air, 5 denotes a blower for the first zone, 6 denotes a blower for the second zone, and 7 denotes an exhaust gas blower, and 8 denotes a deodorizing apparatus.
The paper 2 printed by the printing press is fed into the drying apparatus body 1, and the hot air from the burner 4 is blown onto the paper through the hot air blowing nozzles 3 so that the solvent in ink is evaporated. The hot air, which has been blown onto the paper 2 in the drying apparatus body 1 from the hot air blowing nozzles 3, is returned to the suction side of the blower for the first zone 5 and the blower for the second zone 6, and is then reheated by the burner 4 and sent to the hot air blowing nozzles 3. Part of the hot air is sucked by the exhaust gas blower 7 and sent to the deodorizing apparatus 8, where the gas is deodorized. Part of the deodorized gas is returned to the drying apparatus body 1, and the remnant is discharged into the atmosphere. For pollution prevention, a negative pressure is produced in the drying apparatus body 1 to prevent the hot gas (exhaust gas) in the drying apparatus body 1 from discharging to the outside.
The conventional drying apparatus for a rotary printing press shown in FIG. 13 has the following disadvantages:
(1) The apparatus has a high consumption of fuel because the fuel supplied to the burner 4 is burned to reheat the hot air circulating in the drying apparatus body.
(2) The operation cannot be performed while the amount of exhaust gas is restricted because if the concentration of solvent in the exhaust gas is raised by the restriction of exhaust gas discharged from the deodorizing apparatus 8, the temperature in a catalytic reactor provided in the deodorizing apparatus 8 becomes too high (rises to about 500.degree. C., the upper limit of temperature).
(3) A large-size exhaust gas blower 7 is required. This is because large amounts of outside air (air for combustion) is introduced into the drying apparatus body 1 since the temperature of circulating hot air or the temperature of paper is kept at about 190.degree.-250.degree. C. by controlling the burning conditions of burner 4 disposed in the circulation line, so that large amounts of exhaust gas must be discharged by the exhaust gas blower 7 to maintain the negative pressure in the drying apparatus body 1
(4) The capacity of burner 4 disposed in the circulation line must be 3-5 times higher than the capacity needed for normal operation in order to speed up the startup operation since the rotary printing press is frequently stopped for change of plates.
To solve these problems, the inventors made an invention shown in FIG. 14 (refer to Japanese Patent Application No. 083912/1989 (1-083912)).
In FIG. 14, reference numeral 1 denotes a drying apparatus body, 2 denotes printed paper, 3 denotes a hot air blowing nozzle, 4 denotes a preheating burner, 5 denotes a blower for the first zone, 6 denotes a blower for the second zone, 7 denotes an exhaust gas blower, 8 denotes a direct fired deodorizing apparatus, 9 denotes a heat recovery apparatus, 10 denotes a burner for deodorization, 11 denotes a preheater, 12 denotes a direct fired reactor, 13 denotes a hot air temperature control device for regulating burning at the burner 10 for deodorization for the direct fired deodorizing apparatus 8 based on a value detected by a temperature sensor 16 for the hot air blown from the nozzles, 14 denotes a paper temperature control device for regulating burning at the burner for deodorization 10 in the direct fired deodorizing apparatus 8 based on the value detected by a paper temperature sensor 17, and 15 denotes a selector switch.
At the startup before the normal operation, the exhaust gas blower 7 is activated to draw the outside air (air for combustion) into the drying apparatus body 1. The outside air drawn into the drying apparatus body 1 is directed from the exhaust gas blower 7 to the inside of heat transfer tube of the preheater 11, the direct fired reactor 12, the outside of heat transfer tube of the preheater 11, and the inside of heat transfer tube of the heat recovery apparatus 9 in that sequence.
Also, the outside air drawn into the drying apparatus body 1 is circulated in the drying apparatus body 1 by activating the blower for the first zone 5 and the blower for the second zone 6. Then, the air circulating in the drying apparatus body 1 is heated by igniting and burning the preheating burner 4.
The air in the drying apparatus body 1 is directed as the air for combustion from the exhaust gas blower 7 to the inside of heat transfer tube in the preheater 11 and to the direct fired reactor 12. Then, the fuel for the burner for deodorization 10 is ignited and burned The produced exhaust gas is directed from the outside of heat transfer tube of the preheater 11 to the inside of heat transfer tube of the heat recovery apparatus 9. This exhaust gas, after preheating the air, is discharged out of the drying apparatus body 1. Thus, the circulating air in the drying apparatus body 1 can be heated rapidly to a specified temperature at the startup before the normal operation.
When this condition is established, the preheating burner 4 is turned off to start the normal operation. In the normal operation, the paper 2 printed by the rotary printing press is fed into the drying apparatus body 1, while hot air is blown into the paper passage through the hot air blowing nozzles 3 so that the printed paper 2 is exposed to the hot air and the solvent contained in the ink on the paper is evaporated. The hot air containing the evaporated solvent (exhaust gas of about 140.degree.-170.degree. C.) is returned to the outside of heat transfer tube of heat recovery apparatus 9 at the suction side of the blower for the first zone 5 and the blower for the second zone 6, where the hot air is reheated to about 190.degree.-250.degree. C. by the exhaust gas passing through the inside of heat transfer tube of the heat recovery apparatus 9, namely the exhaust gas fed from the direct fired reactor 12 of the direct fired deodorizing apparatus 8 (exhaust gas of about 400.degree.-500.degree. C.), and directed to the hot air blowing nozzles 3.
Part of the hot air in the drying apparatus body 1 is sucked by the exhaust gas blower 7 and fed into the preheater 11 of the direct fired deodorizing apparatus 8, where part of the hot air is preheated by the exhaust gas from the direct fired reactor 12. Next, the hot air is directed to the direct fired reactor 12 which is heated to about 700.degree.-1000.degree. C. by the burner for deodorization 10, where the evaporated solvent in the hot air is burned for the deodorization of hot air. The exhaust gas produced at this time is directed to the inside of heat transfer tube of the heat recovery apparatus 9 for the above-described heat exchanging and is then discharged out of the drying apparatus body 1.
The heat recovery apparatus 9 can use a shell and tube heat exchanger or a plate type heat exchanger.
When drying is controlled based on the hot air temperature, the set value of deodorizing apparatus furnace temperature on the hot air temperature control device 13 is calculated for correction from the value detected by the blowing hot air temperature sensor 16. Based on the result, the burning amount of the burner for deodorization 10 is controlled, and the temperature of hot air blowing from the nozzles is kept at the set value.
When drying is performed by paper temperature control, the set value of deodorizing apparatus furnace temperature on the paper temperature control device 14 is calculated for correction from the value detected by the paper temperature sensor 17. Based on the result, the burning at the burner for deodorization 10 is controlled, and the temperature of hot air blowing from the nozzles is kept at the set value.
The conventional drying control device for the rotary printing press shown in FIG. 14 has the following disadvantage: since the deodorizing capability of the direct fired deodorizing apparatus 8 relates directly to the furnace temperature of direct fired reactor 12 as shown in FIG. 14, the furnace temperature must be not less than the lower limit T.sub.DL in order to comply with the regulations regarding the odor concentration For the conventional drying control device for the rotary printing press shown in FIG. 14, nevertheless, the furnace temperature of the direct fired deodorizing apparatus 8 is not controlled. For example, in the paper temperature control, when the thermal load is decreased (for example, when the printing speed decreases), the burning amount of the burner for deodorization 10 is decreased, sometimes resulting in a decrease in deodorizing apparatus furnace temperature down to a value less than the lower limit.
In the apparatus disclosed in Japanese Patent Application No. 083912/1989, the controllability is not high because the blowing hot air temperature does not respond to the temperature change in the reaction furnace 12 since the heat capacity of the heat exchanger 9 is high, when a speed change (i.e., thermal load fluctuation) occurs in the printing press or when an attempt is made to change a control target value (instrumental set value) of blowing hot air temperature.
Furthermore, according to this conventional art, the hot air can be heated in about one minute by using the preheating burner 4 at the startup, but the apparatus has no effective mechanism for cooling the hot air when the printing speed is decreased due to troubles or adjustments in the printing press during the normal operation. That is, the responsiveness of paper temperature is very low because the deodorizing apparatus furnace temperature has a lower limit for providing proper deodorizing capability and because the heat capacity of the heat exchanger is high Therefore, the paper temperature exceeds the specified value for a long period of time, resulting in a heavy paper loss.